Process of treating sensitive photographic film



Sept. 16, 1941. M. E. RUSSELL ET AL 2,256,356

PROCESS OF TREATING SENSITIVE PHOTOGRAPHIC FILM Filed April 22, 1938 2 Sheets-Sheet 1 FIG. I. Y

SPEED Y I3 .17 2o MARI ON E. RUSSELL LOYD A. JONES INVENTORS 4 WEEKS AT W v GAMMA Sept M. E. RUSSELL 'E'l AL ,3

. PROCESS OF TREATING SENS ITIVE PHOIOGRAPHIC FILM Filed-April 22, 1938 .2 Sheets-Sheet 2 SPEED FIG. 5.

v JPEED FIG. 5. B

' WEEKS V F IG. 7.

GAMMA 6 7 a s I I0 WEE/"5 MAR/0N E- U boy A. JONES INVENTOR ATTORNEYS Patented Sept. 16, 1941 PROCESS or TREATING SENSITIVE rno'ro- GRAPHIC FILM Marion E. Russell and Loyd A. Jones, Rochester, N. Y., assignors to Eastman Kodak Company,

minor portion. of ;1

Rochester, N. Y., a corporation of New Jersey Application April 22, 1938, Serial No. 203,536

In Great Britain May 27, 1937 7 Claims. (Cl. 95-7) This invention relates to the stabilization ofphotographically sensitive materials of the gelatino silver halide type and'to a product thus treated, the sensitometric characteristics of which, when measured under standard conditions, remain substantially constant.

It has long been known that the, sensitometric characteristics of photographic materials, such as speed, contrast (gamma), tendency to fog and the like, change with age and that, under ordinary atmospheric conditions, such materials in most cases undergo changes in sensitometric characteristics rather rapidly for a period of weeks after manufacture, usually from six to twelve. These tend to become substantially con stant, provided the atmospheric conditions, temperatureand humidity, in which the film is kept, remain. constant.

No method has been hitherto known, however, by which the manufacturer couldbe sure of the sensitometriecharacteristics of the product after it had left his hands and been exposed to the varying conditions of shipping and storage over which he had no control. I

We have discovered that it is possible to make a photographic material, the characteristics of which are stabilized at values which are maintained despite subsequent changes in atmospheric storage conditions and the speed of which is stabilized at a high value, approximately that which it had when first manufactured, and we consider both this novel product, having new and very valuable properties, and the methods by. which this is attained as included within our invention,

When we refer herein to the characteristics of a material as stabilized, we mean that the' retention of such characteristics in'the material, though subjected to storage under any ordinary atmospheric conditions, however variable,- is im- Definite improvements over photographic materials placed in ordinary storage are shown by such materials after being kept under conditions of less than 5% relative humidity, but after storage in a relative humidity of 10%, the material'is scarcely better than when kept under ordinary room humidity'conditions.

The material, if, it is positive motion picture film, may be slit, perforated and wound on reels, and placed in storage chambers containing calcium chloride in suflicient amount to maintain the humidity at the required low level. Other desiccants may be used, such as magnesium perchlorate activated carbon, activated alumina, silica gel, or sulfuric acid.

The moisture may also be removed mechanically; as bycirculating the air through a re-'-- frigerating unit whereby the humidity can be reduced to the desired level, or it may be re-v and other volatiles diffuse from the sensitive tinguished from the mere vacuum packing of thematerial. It has been proposed that photographic material, in the same manner as food products or tobacco, be packed in 'a partial vacuum in order to preserve it. By such methods, substantially all'the moisture and volatile compounds, in

the products were retained, though a portion of the air was removed. In ordinary vacuum packing, the container is submitted for a short time proved and. the characteristics remain morenearly uniform in value than in film not subjected to our treatment, it being understood that the methods of measurement are uniform in all cases.

One way in which this end may be obtained is. by storing the material for an extended period of time in a dry atmosphere. The atmosphere is one which will reduce the moisture content of the material to the equivalent of that obtained when the material is brought into moisture equilibrium with an atmosphere of ordinary room temperature and pressure and a relative humidity of not more than 2% and preferably only a to a partial vacuum' and then sealed, thus tend ing to hold the moisture and other volatile compounds in the product. Because of the very long periods during which we submit photographic products to desiccation, substantially all moisture and other volatiles are removed both from the emulsion layer and from the support..

.The desiccation may be achieved rapidly by subjecting the photographic material for a relatively short time to a relatively high temperature and then maintaining it in this desiccated condition for a predetermined time by any deing it on a'support.

One method which we consider as included original speed.

2 within the scope of our invention is subjecting the film to avery lowtemperature, say 40." F., which is equivalent to the removal of water and other vapors from the sensitive element, and maintaining it at that temperature for a predetermined period. Sincethe vapor pressure falls to a very low value, any effects of moisture and other volatiles in the support and emulsion desiccation does not begin until sometime-after manufacture, during which time the sensitometric characteristics of the product may have changed, the desiccation has a valuable stabilizf ing effect. Under such circumstances, the product will in some cases be stabilized at the speed which it had reached at the start of desiccation, but in many instances its speed increases during the period of desiccation and becomes stabilized at a point which approximates the.

As is to be expected, the effect is not the same with all materials but we have found it particularly satisfactory with such materials as positive motion picture film and other moderate speed materials'such as film used for sound recording, duplicating motion picture images and the like. When photographicplates are subjected to desiccation treatment to stabilize the same, the emulsion. tends to flake or strip from the glass but this tendency can be overcome by the addition of suitable plasticizing materials to the-emulsion.

In carrying out ourinvention, we have found that, after storage under desiccating conditions for a period of three weeks, film loses speed somewhat thereafter when kept in ordinary storage conditions but the speed remains higher and more nearly constant than with film not so treated. The results were even more marked after a period of six weeks while after nine weeks, film of the positive motion picture typewas stabilized and showed no appreciable change insensitometric characteristics with keeping under any subsequent storage conditions. In some instances it is necessary to prolong the desiccation more than nine weeks before the film attains its maximum stabilization. It should be understood that all sensitometrlc measurements were made on film brought to equilibrium with identical atmospheric conditions (that is, temperature and relative humidity).

Since the large motion picture laboratories are air conditioned at standardized humidities and temperatures, the manufacturer can thus, by testing the sensitized product under the atmospheric conditions at which it is to be used, know what its sensitometric characteristics will be when used.

Not only does the stabilized film maintain its sensitometric' characteristics more nearly constant when stored under various atmospheric conditions and expowd after being brought to equilibrium with standard atmospheric conditions, but it also tends to be with different atmospheric con 'tions before exposure to light.

It is to be noted that,.while the speed of the film taken as an example remains substantially assesseconstant, instead of falling during the desiccation period, thecontrast (gamma) of the emulsion may change about as much as it would under ordinary conditions, but becomes stabilized at a definite level; whereas with films not undergoing" prolonged desiccation the contrast is as uncertain as the speed. In other words, the treatment stabilizes both speed and contrast, the former at a higher value than it would otherwise have and the latter at substantially the value which it has at the end of the desiccation period.

We have also found that the tendency to fog is likewise stabilized, that is, this characteristic of a material after treatment as herein described is substantially uniform for a reasonable length of time at the value which it had at the end of the treatment.

It is further to be understood that, while in the description of the sensitometric characteristics of the materials used as illustrative examples, the speed and contrast tend to fall in ordinary storage,- certain materials under certain storage conditions show increases in speed with aging and our invention here also tends to stabilize these properties so that, instead of changing in one direction or the other, they are rendered more nearly uniform.

-A variation of temperature during the treatment period within any limits of ordinary usage makes no substantial difference in the properties of the stabilized film.

We do not know how long the film treated as described will remain stabilized but it is certain that-the condition when obtained remains for many months without deterioration.

In order to illustrate graphically the effects of prolonged desiccat'on, reference is made to the accompanying graphs, which are to be taken as examples of results actually obtained.

Figs. 1 to 7 are graphs showing the. behavior of film under different sets of conditions. For purposes of comparison, the same type of film, namely a positive motion picture film, was chosen. In each of Figures 1 to 5, the ordinates represent speed at an arbitrary unit of measurement and in Figs. 6 and '7, they represent contrast or "gamma and the abscissae in all figures represent time measured in weeks. In the following description and in the drawings where reference is made to specific temperatures andrelative humidity, it is understood that an atmosphere maintained at the values given is referred to.

Since in ordinary manufacturing routine, it would be difiicult to slit, perforate and pack the film in less than several days, the films were not desiccating chamber until they were three days old, and this presumably accounts for more nearly constant when brought to equilibrium ignated A and B) and their drop in speed during the first week.

In each of Figures 1 to 5 a comparison is made among (a) a film placed in the desiccating chamber and kept there constantly at a temperature (b) a film placed in the desiccating chamber at the same time as (a) and kept there for a definite period, (the beginning and end of which are indicated by heavy vertical lines desthen maintained in an atmosphereof 70 F., and 50% RH, (c) a film subjected to the same desiccating treatment as (b) and then maintained at F. and 27% RH, (d) a film, not desiccated at all, and maintained throughout at 70 F. and 50% RH.. j v

In each instance the films were rehumidified before being tested, although our experiments indicate that their speed 'may be the same though rehumidification is not complete.

at 70 F.,

In each figure, the curves corresponding to the conditions enumerated above are indicated respectively as a, b, c and d, the curve 11 being the same in each of Figs. 1 to 5.

In Fig. l, films (a), (b) and (c) were placed 3 that, although the films in the particular 'experi w ments shown lost slightly more in contrast when in the desiccating chamber when three days old and (b) and were removed at the end of three weeks. It will be seen that, so long as the three films remained in the desiccator, after a short interval their speed remained constant, but that after removal it dropped, approaching a constant value higher than that of (d) which had not been desiccated.

Figs. 2 and 3 illustrate the results of the same procedure except that (b) and (0) were removed at the end of six weeks and nine Weeks in the respective figures. It is to be noticed from Figure 3 that after nine weeks, curves at, b, and c are coincident as a straight line.

In Fig.- 3 are also indicated the properties of three films stored like (11) for nine weeks at 70 F. and 50% RH and then kept under different conditions. In this figure e indicates the speed of film kept, after the ninth week at 70 F. and 25% RH;-f, the film then at 50 F. and 50% RH and g, film then kept at 90 F. and 27% RH. Whereas the films (a), (b) and (c) desiccated for nine weeks, have precisely the same speed, despite storage under widely difierentl atmospheric conditions, the films (d), (e), (f), and (g) kept under identical non-desiccating conditions for nine weeks, have widely different speeds when kept in different subsequent storage conditions.

In Figs. 4 and 5 are indicated the results when the films (a), (b) and (c) to be desiccated are not placed in a desiccating atmosphere until several weeks after manufacture, being kept in the meanwhile like film (d) in an atmosphere at with different sensitive products.

the standardized condition 70 F. and 50% RH.

In Fig. 4, the interval after manufacture is three weeks, and in Fig. 5, nine weeks, and in both figures, the films are kept in the desiccating atmosphere for nine weeks. It will be seen that in each case, as in Fig. 3, curves (1,1) and c are identical. Although all the films lost speed in the interval preceding desiccation when kept in the same uniform conditions, it will seen that films (a), (b) and (c) regained a large part of their loss within the nine weeks desiccation pe- In Fig. 7 areshown curves k and 1 representing the change in gamma. in four films all kept for nine weeks in the standard atmospheric condition, '20 F. and-50% RH, and then each kept in,

different atmospheric conditions, which are in dlcated on the respective curves. It is to be noticed from Fig. '7, that the film kept in the same storage conditions holds itscontrast well, as shown by curve is, but that the three others, under different conditions, change their contrast characteristics, the change in all three being approximately identical, as shown by the curve 1 common to all three. It is further to benoticed from a comparison of the two Figures 6 and '7 kept in the desiccating atmosphere than thosekept under standard conditions, they maintained under all conditions the value which they had then attained, while those kept at the standard conditions for nine weeks in contrast varied in contrast when subsequently kept under different atmospheric conditions.

It is to be understood that all measurements were made on film which had been brought into equilibrium with fixed atmospheric conditions of temperature and relative humidity.

While in the above the conditions of storage for each curve shown are uniform following the treatment period, substantiallythe same results are obtained if they change frequently and widely after desiccation.

We' propose to apply this process to all kinds of sensitive photographic materials either of the gelatino silver halide type or those in which sensitive silver halides are carried by other high molecular weight media. Any of these types may beapplied to any suitable base such as paper, film and glass, it being understood that the process will vary as experience dictates depending on the results obtained with difierent products. It is further to be understood that the degree to which different photographic properties, such as speed, contrast, freedom from fog and the like are stabilized varies considerably The term stabilizing as used in the claims (unless modified by other limitations) means producing in photographic materials improved retention of one or more of their sensitometric characteristics though subjected to storage under any normal atmospheric conditions-the methods of measurement (conditioning, exposure, development, etc.) remaining constant.

It is to be remarked'that we consider as within the scope of our invention all methods of attaining the same result, some of which are su ested above, and the improved product resulting therefrom.

Having thus described our invention, what we claim as new and desire to be secured by Letters Patent is:

1; The method of stabilizing sensitometric characteristics of an unexposed protographi cally sensitive emulsion comprising a suitable colloid carrier and silver halide that comprises reducing its water vapor pressure to a point equivalent tothe water vapor pressure existent at less than 5% relative humidity at atmospheric pres- .sure and maintainingit in such condition for at least three weeks.

2. The method of stabilizing sensitometric characteristics of an unexposed photograp'hically sensitive gelatino silver halide emulsion that comprises reducing its water vapor pressure to a point equivalent to the water vapor pressure existent at less than 5% relative humidity at atmospheric pressure and maintaining it in such condition for at least three weeks.

3. The method of stabilizing sensitometric characteristics of an unexposed photographically sensitive emulsion comprising a colloid carrier and silver halide that comprises reducing its moisture content to a value equivalent to that which it would have when in equilibrium with an atmosphere having a relative humidity less than 2% at atmospheric pressure and maintaining it in such condition for at least six weeks.

4. The method of stabilizing sensitometric ment to an atmosphere characteristics 0! an unexposed photoxraphieally sensitive element comprising a gelatino silver halide layer that comprises having a relative humidity of less than 2% for a period of at least three weeks.

5. The method of stabilizing sensitometric characteristics of an unexposed photographically subjecting the elesensitive element comprising -a support and a zelatino silver halide layer that comprises sub- ,iectina the elementto, an atmosphere having a relative humidity of less than 2% for a period of at least six weeks.

6. The method of stabilizing sensitometric characteristics of an unexposed photographicall'y sensitive element comprising a geiatino silver r spheric pressure and room halide layer that comprises subjecting the element to an atmosphere having a relative humidity of less than 2% for a period of at least eight 

